Challenge to Real Climate On The IPCC Global Climate Model Predictions Of Global Warming

SECOND UPDATE: May 27 2008

In seeking further to assess the agreement between the GISS model and observations, since Gavin would not help, I dug deeper into the paper

Hansen et al, 2005 Earth’s Energy Imbalance: Confirmation and Implications, Science 3 June 2005: 1431-1435 DOI: 10.1126/science.1110252

and their supplement.

It is clear that the GISS model is consistent with global average upper ocean heat content changes in the 1990s and up to 2003, and that the Watts per meter squared estimate of radiative imbalance that is diagnosed is accurate based on the observed ocean heat data. One of the confusions in their paper, however, is that Figure 2 has the incorrect units plotted on their left hand axis. The units are plotted as Watts year per meter squared, when they should be Joules *10**22.

The Supplemental data presents insightful plots of the spatial distribution of upper 750 m ocean heat content change. This is an effective format for them to use when updating the observational and modeling comparisons.  This should include quantitative statistical comparisons of the spatial degree of agreement between the GISS model predictions and the observations of upper ocean heat content over the same time period.

The upper ocean heat content change data in the last 4 years, however, does not conform to the Watts per meter squared estimate of radiative heating reported in Hansen et al. 2005.  This is a central issue that needs to be explained by the GISS group. We look forward to Gavin and Jim (and their other co-researchers) reporting to the climate community on this subject. We also look forward to the values of upper ocean heat content changes that the GISS model predicts for the next several years.

UPDATE: MAY 27 2008

Regretfully, Real Climate [Gavin Schmidt] has rejected the challenge [see http://www.realclimate.org/index.php/archives/2008/05/tropical-tropopshere-ii/#comment-88172].  The claim that I should do this analysis is off base, however, as Gavin works with the models and is in an ideal position to do this.

Moreover, Gavin ansd his colleague Jim Hansen already did this a few years ago as I wrote in the first posting of this weblog; again see

Hansen et al, 2005: Earth’s Energy Imbalance: Confirmation and Implications. Science Express. April 28 2005

It is obviously time for GISS to repeat this analysis, since their conclusion on the radiative imbalance is significantly too high. The data were good enough then for Gavin , where as they wrote in the abstract of their paper

“…..Our climate model, driven mainly by increasing human-made greenhouse gases and aerosols, among other forcings, calculates that Earth is now absorbing 0.85 ± 0.15 watts per square meter more energy from the Sun than it is emitting to space. This imbalance is confirmed by precise measurements of increasing ocean heat content over the past 10 years…..”

The data have improved even further since (e.g. see).  The only conclusion is that completing this comparison between GISS modeled and observations of updated upper ocean heat content trends would be an embarrassment to them.

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Real Climate has offered a challenge (a bet) on their weblog on global cooling but they use global average surface temperature trends as the metric [see].

As shown, for example, in

Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335,

however, the monitoring of changes in the ocean heat content is a much more robust metric to assess global warming and cooling. The global average surface temperature trend has a number of unresolved issues with respect to its value to diagnose global climate system heat changes, including a warm bias (see and see).

Climate Science has proposed using Joules that accumulate within the oceans as the currrency to assess climate system heat changes, rather than a global average surface temperature trend (e.g. see).

This viewpoint is supported by Jim Hansen and colleagues.  As reported by

Hansen et al, 2005 Earth’s Energy Imbalance: Confirmation and Implications, Science 3 June 2005: 1431-1435 DOI: 10.1126/science.1110252′

their abstract claims that

“Our climate model, driven mainly by increasing human-made greenhouse gases and aerosols, among other forcings, calculates that Earth is now absorbing 0.85 ± 0.15 watts per square meter more energy from the Sun than it is emitting to space. This imbalance is confirmed by precise measurements of increasing ocean heat content over the past 10 years. Implications include (i) the expectation of additional global warming of about 0.6°C without further change of atmospheric composition; (ii) the confirmation of the climate system’s lag in responding to forcings, implying the need for anticipatory actions to avoid any specified level of climate change; and (iii) the likelihood of acceleration of ice sheet disintegration and sea level rise.”

This means, using the conversion between a continuous rate of the global average heating in Watts per square meter and the accumulated Joules of heat given in the Pielke 2003 paper, that the 0.85 Watts per meter squared reported in Hansen et al correponds to an accumulation of heat of  1.38 * 10**22 Joules per year. Over ten years, this would be 13.8* 10 ** 22 Joules of heat accumulation. The use of this climate metric (Joules) to assess global warming and cooling will add to the resolution of the very appropriate issues raised on Prometheus and The Blackboard as to how to test the skill of the IPCC models.

On those websites, the discussion has focused on how many years temperatures at one level near the surface must be monitored in order to have confidence that model predictions of the global average surface temperature trend are consistent with the observations of temperature trends.  The use of Joules, however, significantly reduces the time period required, since it a change in a reservoir of heat (i.e. in the ocean) with its much greater mass that is sampled, rather than the trend of the global average near-surface air temperature anomaly at one level.

The challenge to Gavin Schmidt and Ray Pierrehumbert at Real Climate (since Real Climate has presented a bet), therefore, is to answer these questions:

  • what amount of heat in Joules was predicted by the IPCC models to accumulate within the climate system over the last five, ten and twenty years?
  • what is the best estimate of what actually accumulated based on the observations of ocean heat content changes for these three time periods?
  • what magnitude of heat accumulation in Joules in the next five, ten, and twenty years would cause Real Climate to conclude that the IPCC models are “inconsistent” with the observations?

We would be glad to post their reply to these questions as a guest weblog on Climate Science.

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